The Internet Engineering Task Force (IETF) Request for Comments (RFC) 3031 specifies a multiprotocol label switching (MPLS) architecture. The MPLS architecture in RFC 3031 permits packets entering a network to be assigned by an ingress router to a prescribed “Forwarding Equivalence Class” (FEC): once a packet has been assigned to a specific FEC (identifiable by a “label” added to the packet), the packet can be forwarded with its corresponding assigned label to a next hop label switching router (LSR). The next hop LSR can use the label supplied with the packet as an index to locate a forwarding table entry that specifies the next hop, and a new label used by the corresponding next hop LSR for the corresponding FEC and which replaces the label in the received packet. Hence, the next hop LSR replaces the label in the received packet with its new label, and forwards the packet on the next hop specified in the table, resulting in forwarding the packet via a label switched path (LSP) without the necessity of executing other routing algorithms based on parsing the network layer protocol header (e.g., the Internet Protocol (IP) header). RFC 3036 specifies a label distribution protocol (LDP) that enables label switching routers to exchange label bindings, enabling the label switching routers to map network-layer routing information directly to data-link layer switched paths.
The Internet Draft by Minei et al., “Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths,” draft-ietf-mpls-1dp-p2mp-02, June 2006, describes extensions to the label distribution protocol specified in RFC 3036 for establishing multipoint-to-multipoint LSPs between label switching routers having established a tree topology with a single root and one or more leaf nodes, where the leaf nodes can operate as ingress nodes for inserting traffic into a network, and/or egress nodes for outputting traffic from the network, without requiring use of any multicast routing protocol within the network. In contrast, a point-to-multipoint LSP has one ingress label switching router and one or more egress label switching routers, and a multipoint-to-point LSP has one or more ingress label switching routers and one unique egress label switching router.